The key thing to note is the time it takes you to transition from Heavy Thrust over to Impulse Drive and the Jump you use in the middle of it.
You might spend something like half a second or more going from the flank to the rear of an enemy so make sure that this is done inbetween the Global Cooldown - for instance, RIGHT after you use Heavy Thrust, start moving to the rear (pray your tank stays still). This way, once you're able to use Impulse Drive, you can use it right away instead of getting into position.
Your Jump right after Chaos Thrust is in a place where you'll lose out on something like half a second or more by the entire animation taking so long to wind up and wind down.
These two things are probably where your 1.5 seconds is going/being used up - yeah, dropping Fracture would solve it too but I like the idea that more DoTs = better failsafe if something goes wrong (such as being in a Pick Up Group and the Tank just doesn't sit still or is in a bad position etc.)